Life Assessment by Monitoring Biaxial Strain-Rates in High Temperature Steam Pipelines

Most of the main coal fired stations in the UK are operating beyond their original design life and it is essential to be able to manage the integrity of the high temperature pipework systems, for both commercial and safety reasons. The fossil fired plant in the UK has operated flexibly for a number of years, which complicates the remanent life assessment of a pipework system. This paper specifically addresses monitoring the creep strain accumulation over time of high temperature pressurized steam pipes in order to better quantify the remanent life and thereby provide improved advice on run/repair/replace issues. Any monitoring instrumentation needs to be rugged and able to endure what is a hostile environment and provide reliable strain measurements in both the longitudinal and circumferential directions of the pipe. This paper presents one monitoring method that has been developed for service use. The monitoring system uses a specially designed strain gauge that carries optical targets, image capture and analysis is used to determine the in-service creep strain rates. Experiences from site installations will be described.